Effects Of Dietary Cobalt Levels On Growth Performance,metabolic Performance And Hair Follicle Development Of Growing Rex Rabbits

The experiment was conducted to investigate the effects of dietary Cobalt levels on production performance,metabolic performance and hair follicle development of growing Rex rabbits by single factor experiment.Two hundred growing rex rabbits were randomly assigned into 5 groups with 40 replicates in each group and each replicate contained 1 rabbit.Rabbits in 5 groups were fed basal diets supplemented with 0,0.1,0.4,1.6,6.4 mg/kg cobalt,respectively.The trial lasted for 7 days for adaptation and 53 days for test.The results showed as follows:(1)Dietary cobalt supplemental level had significant influence on end body weight(EBW)and average daily feed intake(ADI)(P<0.01),but had no significant influence on average daily gain(ADG),feed/gain(F/G),eviscerated ratio,half eviscerated ratio,meat quality,thymus index,spleen index,liver index,intestinal villus height,crypt depth and V/C(P>0.05).With the increase of dietary cobalt supplemental level,EBW,ADG,half eviscerated ratio,thymus indexes and duodenum villus height tended to be increased firstly and then decreased,and the highest appeared in 0.4 mg/kg group.(2)Dietary cobalt supplemental level had no significant influence on fecal nitrogen(FN),digestible nitrogen(DN),DN/IN,RN/DN,serum total protein(TP)and albumin(ALB)(P>0.05);had significant influence on nitrogen intake(NI),urinary nitrogen(UN),nitrogen retention(RN),RN/IN(P<0.05),with the increase of dietary cobalt supplemental level,NI、RN and RN/IN tended to be decreased firstly and then increased,UN tended to decreased,and the highest appeared in 0.4 or 1.6 mg/kg group.Dietary cobalt supplemental level had significantly influence on activity of trypsin(P<0.05),the highest appeared in 0.4mg/kg group.Dietary cobalt supplemental level had significantly influence on serum urea(UR)(P<0.05),with the increase of dietary cobalt levels UR tended to be increased firstly and then decreased,the highest appeared in 0.4 mg/kg group.Dietary cobalt supplemental level had significant influence on the content of cobalt in fecal,urine,serum,muscle,liver,spleen,kidney(P<0.05),with the increase of dietary cobalt supplemental level,all the content of cobalt increased.(3)Dietary cobalt supplemental level had no significantly influence on fur area,fur weight and fur thickness(P > 0.05),with the increase of dietary cobalt levels fur weight tended to be increased firstly and then decreased,the highest appeared in 0.4 mg/kg group.Dietary cobalt supplementation on Rex rabbit had a significant effect on hair length and hair follicle density(P<0.05),and the co addition level is 0.4 mg/kg when the most with the increase of the level of cobalt in the diet,the density of hair follicles showed a trend of first increasing and then decreasing.When the level of 6.4mg/kg was increased,the density of hair follicles was the lowest.Selected cobalt content of 0 and 6.4 mg/kg groups were analyzed by fluorescence quantitative analysis and Western Blotting technology,the results found that dietary cobalt supplementation had significant effects on Tyrosinase,BMP2,BMP4(P<0.05),and high cobalt diets than low cobalt diets expression level increased,showed that Tyrosinase,BMP2,BMP4 involved in the regulation of hair follicle and AMPK,Wntlob signaling pathway is involved in the regulation of hair follicle without cobalt.In conclusion,appropriate dietary cobalt supplemental level is 0.4 mg/kg for growing Rex rabbit(dietary cobalt measured content are 0.60 mg/kg),Where the cobalt addition of 6.4mg /kg when the Rex has a slight poisoning symptoms.